Control instrument

ABSTRACT

In a control instrument, a switch embodying an actuating element, an arm arranged to effect actuation of the actuating element, said arm having an arcuate portion against which the actuating element is held, a support mounting the arm for movement about a pivot axis located at the center of curvature of said arcuate portion and for movement relative to said pivot axis, a transmitter supported with an end adjacent the arm, said transmitter being operable to move the arm relative to said pivot axis to effect actuation of said actuating element, and a cam operably associated with the arm adapted to effect movement of the arm about said pivot axis relative to said transmitter to select the conditions for which the transmitter will become operative to effect actuation of said actuator element.

i United States Patent [191 Reis [ 1 June 5, 1973 [54] CONTROL INSTRUMENT Robert D. Reis, l-lingham, Mass.

[73]. Assignee: United Electric Controls Company, Watertown, Mass.

[22] Filed: Jan. 24, 1972.

[2]] Appl. No.2 220,224

[75] inventor:

[52] US. Cl. ..74/469, 200/56, 200/153 [51] Int. Cl. ..G05g l/00 [58] Field of Search ..74/469, 101;

[56] References Cited UNITED STATES PATENTS 2,595,8l3 5/1952 Raney .;....52/469 Primary ExaminerMilton Kaufman Attorney Robert T. Gammons, Sewall P. Bronstein and John D. Woodberry 57 ABSTRACT In a control instrument, a switch embodying an actuating element, an arm arranged to effect actuation of the actuating element, said arm having an arcuate portion against which the actuating element is held, a support mounting the arm for movement about a pivot axis located at the center of curvature of said arcuate portion and for movement relative to said pivot axis, a

transmitter supported with an end adjacent the arm, said transmitter being operable to move the arm relative to said pivot axis to effect actuation of said actuating element, and a cam operably associated with the arm adapted to effect movement of the arm about said pivot axis relative to said transmitter to select the conditions for which the transmitter will become operative to effect actuation of said actuator element.

1 1 Claims, 3 Drawing Figures CONTROL INSTRUMENT BACKGROUND OF THE INVENTION This invention relates to controls of the kind shown in US. Pat. No. 3,537,317, in which linkage is movable in response to a change in pressure or temperature to actuate a switch or valve and simultaneously to move an indicator over a dial and comprises improvements in SUMMARY In a control instrument, means embodying an actuating element, an arm arranged to effect actuation of the actuating element, means pivotally supporting the arm with an end in engagement with said actuating element, said arm having an arcuate portion, the center of curvature of which coincides with the pivot axis of said supporting means, means pivotally supporting the arm for movement of said arcuate end portion relative to said pivot axis, a transmitter supported with an end adjacent the arm, said transmitter being operable to move the arm relative to said pivot axis to effect actuation of said actuating element, and means operably associated with the arm adapted to effect movement of the arm about said pivot axis relative to said transmitter to select the condition for which the transmitter willbecome operative to effect actuation of said actuating element. The means which is to be operated may be a switch or valve with an actuating pin operable to activate or deactivate the switch or valve. The support comprises an elongate member pivoted at one end for angular movement relative to its pivot, to the opposite end of which the arm is pivotally mounted at one end for movement of its arcuate end about the pivot axis of the support. The transmitter comprises a rod supported with an end adjacent the arm intermediate its ends and with its other end engaged with an arm supported in engagement with a part movable by a motor operable in response to a pressure or temperature change. The means for effecting movement of the support about its pivot axis to displace the arm relative to the transmitter rod comprises a cam supported adjacent the support for rotation relative thereto against which the arm is yieldably held by a spring. The instrument is provided with a dial and a pointer fixed to the cam which is movable thereby relative to the face of the dial to indicate the condition for which operation of the switch or valve is desirably to take place. A second pointer movable by movement of the transmitter relative to the face of the dial indicates theprogress of the change inpressure or temperature toward the place selected for operation.

The invention will now be described in greater detail with reference to the accompanying drawings wherein:

FIG. 1 is a front elevation of the control with parts in elevation and section;

FIG. 2 is a section taken on the line 2-2 of FIG. 1; and y l FIG. 3 is a fragmentary view, to larger scale, of the linkage embodying the invention removed from the instrument with the component parts illustrated partly in elevation and partly in section.

The invention as herein illustrated comprises a novel linkage 10 mounted in an instrument box 12 which is responsive to a change in pressure or temperature communicated thereto through an expandable device 14 to effect operation of switches S1 and S2 mounted in a switch box 16 secured to the top of the instrument box, the instrument box being provided with a dial 18 and two pointers 20 and 22, the pointer 20 being adapted to be placed at a position indicative of the condition selected for actuation of the switches and the pointer 22 being movable in response to the pressure or temperature change to show the approach to the condition selected for such actuation. Valves provided with actuating elements may be substituted for the switches or a switch and valve may be actuated.

The instrument box is of rectangular construction having a back wall 24, forwardly projecting side walls 26-26 and forwardly projecting bottom and top walls 28 and 30. The switch box 16 is of circular section having a back 34, a forwardly projecting side wall 36 which is open at the 'front, and threading 38 peripherally thereof for receiving a closing cap 40. A boss 42 is formed integral with the lower side of the side wall 36 through which there is an opening 44 for receiving the upper end of a threaded sleeve 46, the lower end of which extends through an opening 48 in the upper wall 30 of the instrument box. Threaded nuts 50 and 52 inside the switch box and the instrument box screwed onto the threaded ends of the sleeve rigidly secure the two boxes to each other.

The switches S1 and S2 are microswitches and are secured by a bracket member 54 to the inner side of the wall 36 of the switch box in a position in which their actuating elements 56, 58 are situated substantially on the vertical diameter of the switch box. A bracket member 60 is fastened to the inside of the wall 36 below the switches S1 and S2 on which there is pivotally mounted an actuator element 62, the latter having a portion 64 substantially parallel to the lower side of the switches on which there are mounted an adjustable pin 66 and a fixed pin 68. The adjustable pin 66 is threaded through the part and has at its lower end a head 70 by means of which it may be rotated to adjust its posit ion with respect to the actuating element 56 of the switch S1. A rod 72 is mounted in the sleeve 46 for vertical movement therein, the upper end of the rod being situated adjacent the underside of the part 64, the latter being yieldably held engaged with the upper end of the rod by spring means 72 which holds it away from the lower ends of the switch actuators 56 and 58. The lower end of the rod 72 extends through the opening in the top wall 30 of the instrument box and has threaded to it a sleeve 76, into the lower end of which is threaded a screw 78 provided with a head 80.

Within the instrument box there is a fixed boss 82 which projects forwardly from the back of the box in.

which there is mounted a pin 84, the latter projecting forwardly in a horizontal position and on this pin there is pivotally mounted a bar 86 which extends from the pin transversely across the box directly below the head at the lower end of the screw 78. Movement of the bar 86 in a counterclockwise direction, as shown in FIG. 1, by engagement with the head 80 will move the rod 72 upwardly and this in turn will move the arm 62 upwardly to first actuate the switch S1 and thereafter the switch S2, the arrangement being such as to enable initiating an operation and thereafter terminating the 3 operation, or, for example, initiating an operation and altering the operation.

The particular use of this device for control is to provide for setting the control mechanism to cut-off at a predetermined pressure or temperature, visually indicate on the scale the selected point of cut-off and provide a movable indicator which will indicate the progress of the operation toward the aforesaid point of cutoff. As earlier stated, the device is responsive to temperature and/or pressure changes by way of an expandable motor 14, expansion of which is communicated to the instrument by a rod 88 projecting upwardly through an opening 90 in the bottom wall 28.

A frame 92 is mounted within the box beneath the bar 86 and secured therein by screw-threaded bolts 94, the frame providing support for the control linkage. At the top of the frame, at the right-hand side, there is a boss 96 within which there is fixed a forwardly projecting pin 98, the forward end of which is supported by a plate 100 mounted at its center on a boss 102 projecting forwardly from the frame parallel to the pin 98. An elongate support 104 is pivotally mounted on the pin 98 and extends therefrom laterally across the instrument box toward the left-hand side. At the center of the frame there is a forwardly projecting circular housing 106 having a diametrical front wall, peripherally of which there is a groove 108. A flat cam plate 110 containing a central opening 112 is mounted on the end of the housing in the groove for rotation about its center by means of an overlying spring element 114 secured to the housing by screws ll6l16 extending through holes 115-115 in the element 114 and into threaded holes in the front wall. The cam plate 110 has an eccentric edge 118, the edge being located below the support 104 substantially midway between its opposite ends. A nub 120 on the support 104 directly above the edge of the cam is held engaged therewith by a spring 122, one end of which is connected to the support and the other end of which is connected to the bottom of the frame. A short, forwardly projecting arm 124 at the bottom of the cam plate supports a diametrically disposed arm 126 to which there is secured the pointer and a knob 128. The knob is adapted by rotation to rotate the cam and simultaneously rotate the pointer 20 over the face of the dial 18. The arm 126 is spaced from the face of the cam and the dial 18 which comprises a substantially rectangular plate mounted on the frame between the cam and the pointer and secured in place by screws l30130 screwed into bosses 140-140 extending forwardly from the back of the frame. Rotation of the cam will rock the arm angularly about its pivot axis.

At the distal end of the support 104 there is pivotally mounted one end of an arm 132, the latter extending from the distal end of the support 104 transversely across the instrument box to the proximal end thereof and at its proximal end it has a portion 134 provided with a lower flat edge 136 whichrests upon the upper side of the support 104 and an arcuate portion 138 which engages the underside of the bar 86. The center of curvature of the arcuate portion 138 coincides with the pivot axis 98 of the support 104 so that angular movement of the support 104 rocks the arcuate portion 138 beneath the bar 86 without displacing it. The arm 132 is movable relative to the support 104 an amount limited by engagement of a pin 140 fixed to the support 104 within an arcuate slot 142 in the arm 132.

Movement of the arm 132 relative to the support 104 is effected by a transmitter rod 144 supported in diametrically'disposed openings 146, 148 in the housing 106 with its upper end adjacent the underside of the arm 132 and its lower end resting on a lever 150, the latter being pivotally supported at one end between the frame and the plate on a pin 152 and extending therefrom transversely of the instrument box beneath the housing 106. Elevation of the lever 150 will raise the transmitter rod 144 which, in turn, will raise the arm 132 about its pivot axis relative to the support 104 and such relative movement, by displacement of the arcuate portion 138 relative to the pivot axis 98, will raise the bar 86. A nub 133 at the underside of the arm 132 provides for substantial point engagement of the transmitter rod with the arm.

By adjusting the position of the cam the distance that the transmitter rod has to travel before it engages the arm 132 may be adjusted so as to determine the point at which the arm 132 will be moved relative to the support and in turn effect operation of the switch S2. It is evident by rotating the cam the support may be moved away from the end of the transmitter rod so that the latter will have to travel in greater distance or toward the transmitter rod so that it will have to travel a lesser distance in response to a pressure or temperature change to cause the am 132 to operate the switch S2.

The transmitter rod 144 has on it within the housing 106 a rack 154 which meshes with a pinion 156 which in turn is operable to rotate the pointer 22 over the face of the dial. Thus as the transmitter rod is moved the pointer 22 will indicate the progress of the change in temperature or pressure toward the predetermined selected condition for operation and when it coincides with the pointer 20 or moves beyond it that the operation has been terminated or altered.

The arm rests against the upper end of the member 88 and its operation follows the dictates of the pressure motor 14. An adjustable pin 154 is threaded through a boss 156 on the frame above the distal end of the arm 150 so as to limit its upward movement.

The pin 66 is adjusted to effect actuation of the switch S1 to initiate, terminate or alter an operation. The pin 68 which is not adjusted effects actuation of the switch S2 to initiate, terminate or alter theoperation, the two switches being actuated in sequence, the switch S1 first and the switch S2 second. The aforesaid linkage allows for wide variation in temperature and pressure changes between the actuation of the switch S1 and the switch S2 without a corresponding long travel of the actuator for the switch S1. This characteristic of the linkage is useful in other embodiments where it is desirable to translate movement to a part which has a limited range of movement by means of a part which has a wide range of movement.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents falling within the scope of the appended claims.

I claim:

1. In a control, an element to be actuated, a part having an arcuate portion, means supporting the part with the arcuate portion in engagement with the element for movement of the arcuate portion about a predetermined axis located at the center of curvature of the arcuate portion and for movement of the arcuate'portion relative to said predetermined axis, means movable relative to the part to efiect itsmovement relative to said axis, and means for effecting movement of the part relative to the last-named means about said predetermined axis to select the extent of movement of said last-named means necessary to effect operation of said element.

2. In a control, an element to be actuated, an arm having an arcuate portion, means supporting the arm with the arcuate' portion in engagement with the element for movement of the arcuate portion about a predetermined axis located at the center of curvature of said arcuate portion and for movement of the arcuate portion relative to said predetermined axis, a part supported for movement into engagement with the arm at a distance from said predetermined axis for effecting movement of the arm and said arcuate portion relative to said axis, and a cam with which the arm is engaged operable to move the arm about said predetermined axis relative to said part to select the extent of movement of said part necessary to effect operation of said element. 7

3. In a control, an element to be actuated, an arm having an arcuate portion, means supporting the arm with the arcuate portion in engagement with the element for movement of the arcuate portion about a predetermined axis located at the center of curvature of the arcuate portion and for movement of the arcuate portion about an axis spaced from and parallel to said predetermined axis, a member movable in response to variable conditions relative to said arm to effect movement about the second-named axis, and a cam with which the support is held engaged operable to move the arm about said predetermined axis relative to said member to select the condition at which said arm will be effective to operate said element.

4. In a control, an element to be actuated, an arm having an arcuate portion, a support mounting the arm with the arcuate portion engaged with said element for movement of said arcuateportion about a predetermined axis situated at the center of curvature of said arcuate portion and for movement of the arcuate portion about an axis spaced from and parallel to said predetermined axis, a transmitter rod supported intermediate said axes for movement into engagement with the arm to effect movement of the arm on said support about said axis spaced from said predetermined axis, and a cam supported in engagement with the support intermediate said axes operable to displace the support and hence the arm relative to the transmitter rod about said predetermined axis to select the condition at which said arm will become effective to operate'said element.

5. In a control instrument, a switch, means including an actuating element for actuating said switch, an arm arranged in engagement with said means, said arm embodying an arcuate portion against which said means is held, means supporting the arm for movement about a predetermined pivot axis located at the center of curvature of said arcuate portion and for movement relative to said predetermined pivot axis, a rod supported with an end adjacent said arm for movement into engagement with said arm toeffect said relative movement thereof, and means operably associated with said arm adapted to effect movement of said arm about said predetermined pivot axis relative to said rodto select the condition for which the rod will become operative to effect actuation of said actuating element.

6. In a control instrument, means embodying an actuating element, an arm, means pivotally supporting the arm with an end in engagement with said first-named means, said end having an arcuate portion, the center of curvature of which coincides with said pivot axis of said arm, means pivotally supporting the arm for movement of said arcuate portion relative to said pivot axis of said arm, a transmitter supported with an end adjacent said arm, said transmitter being operable to move said arcuate portion relative to said second-named pivot axis to effect actuation of said actuating element, and means operably associated with said arm adapted to effect movement of said arm about said secondnamed pivot axis relative to said transmitter to select the condition for which the transmitter will become operative to effect actuation of said actuating element.

7. In a control instrument, means embodying an actuating element, an elongate support, means pivotally mounting the support at one end for angular movement about a predetermined axis, an elongate arm, means pivotally mounting the arm at one end atthe distal end of said elongate support with its distal end resting on the proximal end of said support, said arm having at its distal end an arcuate portion, the radius of curvature of which coincides with the pivot axis of said support and which engages said first-named means, a transmitter rod supported with one end confronting said arm intermediate its ends, said transmitter rod being operable by movement to effect angular movement of said arm relative to said support, and means operably associated with the support adapted to effect angular movement thereof about said predetermined pivot axis to displace said arm relative to the end of the transmitter rod predetermined variable distances.

8. In a control instrument, means embodying an actuating element, an elongate support, means pivotally mounting the support at one end for angular movement about a predetermined axis, an elongate arm, means pivotally mounting said arm at one end on the distal end of the elongate support with its distal end resting on the proximal end of the support, said arm having at its distal end an arcuate portion, the radius of curvature of which coincides with said predetermined pivot axis of the support, in engagement with said means, a transmitter rod supported with an end confronting said arm intermediate its ends, said transmitter rod being operable by movement to effect angular movement of said arm on the support relative to said predetermined pivot axis of the support, a cam member supported adjacent said arm intermediate its ends, and means yieldably holding said arm engaged with said cam member, said cam member being operable to displace the arm angularly about said predetermined axis variable distances from the end of the transmitter rod.

9. In a control instrument,.means embodying an actuating element, an arm, means pivotally supporting the arm with an end in engagement with said actuating element, said end having an arcuate portion, the center of curvature of which coincides with said pivot axis of the arm, means pivotally supporting the arm for movement relative to said first-named pivot axis, a transmitter rod supported with an end adjacent said arm, said transmitter rod being operable to move the arm relative to said second-named pivot axis to effect actuation of said actuating element, a dial embodying a scale of indicia, representing a range of conditions, a pointer operably associated with said transmitter rod for movement along said scale, means operably associated with said arm adapted to effect movement of said arm about said first-named pivot axis relative to said transmitter rod to set the arm at a predetermined distance from said end of the transmitter rod, and a pointer operably associated with said last means movable thereby along said scale to indicate the condition thereon selected for movement of the arm relative to said first-named pivot axis in response to movement of the transmitter rod to effect actuation of said actuating element.

10. In a control instrument, a pair of operable devices, each having an actuatable element for effecting its operation, means supported adjacent said actuatable elements for effecting their operation successively, and linkage operable to effect operation of said means to actuate one of the devices and thereafter, to effect operation of the other, said linkage comprising a support pivotally supported at one end, an arm pivotally supported on the other end of the support, said arm having an arcuate portion on which said means rests, the center of curvature of said arcuate portion coinciding with the pivot axis of the support so that angular movement of the support about its pivot axis rotates the arcuate portion about said center without displacing said means, and a cam supported adjacent the support with which the support is held engaged, said cam being operable to effect movement of the support about said pivot axis to displace the arcuate portion of the arm relative to said pivot axis to in turn effect movement of said means.

11. A linkage for moving a part a predetermined distance in response to movement of a variably movable actuator, comprising an arm having an arcuate portion, means pivotally mounting the arm for angular movement about an axis coinciding with the radius of curvature of said arcuate portion, with the arcuate portion engaged with said part, means pivotally supporting the arm at the other end for angular movement about said end to displace the arcuate portion relative to said pivot axis, a transmitter supported with an end adjacent said arm intermediate its ends movable to effect move ment of the arm to displace the arcuate portion relative to said pivot axis, and means for adjusting the position of said arm about its pivot axis in reference to the actuator to control the effective movement of the transmitter while in engagement with the arm to effect displacement of the latter said predetermined distance. 

1. In a control, an element to be actuated, a part having an arcuate portion, means supporting the part with the arcuate portion in engagement with the element for movement of the arcuate portion about a predetermined axis located at the center of curvature of the arcuate portion and for movement of the arcuate portion relative to said predetermined axis, means movable relative to the part to effect its movement relative to said axis, and means for effecting movement of the part relative to the last-named means about said predetermined axis to select the extent of movement of said last-named means necessary to effect operation of said element.
 2. In a control, an element to be actuated, an arm having an arcuate portion, means supporting the arm with the arcuate portion in engagement with the element for movement of the arcuate portion about a predetermined axis located at the center of curvature of said arcuate portion and for movement of the arcuate portion relative to said predetermined axis, a part supported for movement into engagement with the arm at a distance from said predetermined axis for effecting movement of the arm and said arcuate portion relative to said axis, and a cam with which the arm is engaged operable to move the arm about said predetermined axis relAtive to said part to select the extent of movement of said part necessary to effect operation of said element.
 3. In a control, an element to be actuated, an arm having an arcuate portion, means supporting the arm with the arcuate portion in engagement with the element for movement of the arcuate portion about a predetermined axis located at the center of curvature of the arcuate portion and for movement of the arcuate portion about an axis spaced from and parallel to said predetermined axis, a member movable in response to variable conditions relative to said arm to effect movement about the second-named axis, and a cam with which the support is held engaged operable to move the arm about said predetermined axis relative to said member to select the condition at which said arm will be effective to operate said element.
 4. In a control, an element to be actuated, an arm having an arcuate portion, a support mounting the arm with the arcuate portion engaged with said element for movement of said arcuate portion about a predetermined axis situated at the center of curvature of said arcuate portion and for movement of the arcuate portion about an axis spaced from and parallel to said predetermined axis, a transmitter rod supported intermediate said axes for movement into engagement with the arm to effect movement of the arm on said support about said axis spaced from said predetermined axis, and a cam supported in engagement with the support intermediate said axes operable to displace the support and hence the arm relative to the transmitter rod about said predetermined axis to select the condition at which said arm will become effective to operate said element.
 5. In a control instrument, a switch, means including an actuating element for actuating said switch, an arm arranged in engagement with said means, said arm embodying an arcuate portion against which said means is held, means supporting the arm for movement about a predetermined pivot axis located at the center of curvature of said arcuate portion and for movement relative to said predetermined pivot axis, a rod supported with an end adjacent said arm for movement into engagement with said arm to effect said relative movement thereof, and means operably associated with said arm adapted to effect movement of said arm about said predetermined pivot axis relative to said rod to select the condition for which the rod will become operative to effect actuation of said actuating element.
 6. In a control instrument, means embodying an actuating element, an arm, means pivotally supporting the arm with an end in engagement with said first-named means, said end having an arcuate portion, the center of curvature of which coincides with said pivot axis of said arm, means pivotally supporting the arm for movement of said arcuate portion relative to said pivot axis of said arm, a transmitter supported with an end adjacent said arm, said transmitter being operable to move said arcuate portion relative to said second-named pivot axis to effect actuation of said actuating element, and means operably associated with said arm adapted to effect movement of said arm about said second-named pivot axis relative to said transmitter to select the condition for which the transmitter will become operative to effect actuation of said actuating element.
 7. In a control instrument, means embodying an actuating element, an elongate support, means pivotally mounting the support at one end for angular movement about a predetermined axis, an elongate arm, means pivotally mounting the arm at one end at the distal end of said elongate support with its distal end resting on the proximal end of said support, said arm having at its distal end an arcuate portion, the radius of curvature of which coincides with the pivot axis of said support and which engages said first-named means, a transmitter rod supported with one end confronting said arm intermediate its ends, said transmitter rod being operable by movement to effect angular movement of saId arm relative to said support, and means operably associated with the support adapted to effect angular movement thereof about said predetermined pivot axis to displace said arm relative to the end of the transmitter rod predetermined variable distances.
 8. In a control instrument, means embodying an actuating element, an elongate support, means pivotally mounting the support at one end for angular movement about a predetermined axis, an elongate arm, means pivotally mounting said arm at one end on the distal end of the elongate support with its distal end resting on the proximal end of the support, said arm having at its distal end an arcuate portion, the radius of curvature of which coincides with said predetermined pivot axis of the support, in engagement with said means, a transmitter rod supported with an end confronting said arm intermediate its ends, said transmitter rod being operable by movement to effect angular movement of said arm on the support relative to said predetermined pivot axis of the support, a cam member supported adjacent said arm intermediate its ends, and means yieldably holding said arm engaged with said cam member, said cam member being operable to displace the arm angularly about said predetermined axis variable distances from the end of the transmitter rod.
 9. In a control instrument, means embodying an actuating element, an arm, means pivotally supporting the arm with an end in engagement with said actuating element, said end having an arcuate portion, the center of curvature of which coincides with said pivot axis of the arm, means pivotally supporting the arm for movement relative to said first-named pivot axis, a transmitter rod supported with an end adjacent said arm, said transmitter rod being operable to move the arm relative to said second-named pivot axis to effect actuation of said actuating element, a dial embodying a scale of indicia, representing a range of conditions, a pointer operably associated with said transmitter rod for movement along said scale, means operably associated with said arm adapted to effect movement of said arm about said first-named pivot axis relative to said transmitter rod to set the arm at a predetermined distance from said end of the transmitter rod, and a pointer operably associated with said last means movable thereby along said scale to indicate the condition thereon selected for movement of the arm relative to said first-named pivot axis in response to movement of the transmitter rod to effect actuation of said actuating element.
 10. In a control instrument, a pair of operable devices, each having an actuatable element for effecting its operation, means supported adjacent said actuatable elements for effecting their operation successively, and linkage operable to effect operation of said means to actuate one of the devices and thereafter, to effect operation of the other, said linkage comprising a support pivotally supported at one end, an arm pivotally supported on the other end of the support, said arm having an arcuate portion on which said means rests, the center of curvature of said arcuate portion coinciding with the pivot axis of the support so that angular movement of the support about its pivot axis rotates the arcuate portion about said center without displacing said means, and a cam supported adjacent the support with which the support is held engaged, said cam being operable to effect movement of the support about said pivot axis to displace the arcuate portion of the arm relative to said pivot axis to in turn effect movement of said means.
 11. A linkage for moving a part a predetermined distance in response to movement of a variably movable actuator, comprising an arm having an arcuate portion, means pivotally mounting the arm for angular movement about an axis coinciding with the radius of curvature of said arcuate portion, with the arcuate portion engaged with said part, means pivotally supporting the arm at the other end for angular movement about said end to displace the Arcuate portion relative to said pivot axis, a transmitter supported with an end adjacent said arm intermediate its ends movable to effect movement of the arm to displace the arcuate portion relative to said pivot axis, and means for adjusting the position of said arm about its pivot axis in reference to the actuator to control the effective movement of the transmitter while in engagement with the arm to effect displacement of the latter said predetermined distance. 